(a) Field of the Invention
The present invention concerns a keyboard apparatus for use in electronic musical instruments such as electronic organs, which is arranged to provide, by a simple structure, a key touch resembling what is obtained in ordinary pianos.
(b) Description of the Prior Art
The keyboard apparatuses which have been provided so far in conventional electronic musical instruments as electronic organs are such that the sense of key touch differs markedly from the sense of key touch in pianos which are natural musical instruments. Therefore, those who have practiced playing the conventional electronic musical instruments have some difficulty in quickly complying themselves to the playing on a piano, and thus these persons have been unable to make a smooth switch-over of key-operation mode to playing a piano. This is because of the following reasons. The keyboard apparatus of a conventional electronic musical instrument is arranged so as to operate keys against the spring force of a tension coil spring, or a compression coil spring, or a U-shaped spring as the case may be which is provided on the keys. Therefore, unlike the action of the keyboard apparatus of a piano which is operative that, during the course of a key depression, the jack is temporarily progressively dislocated from the butt or from the hammer shank, and also that thereafter the reaction force applied to the player's finger suddenly diminishes, the keyboard apparatus of the conventional electronic musical instrument is operative so that, as the key is depressed down progressively, the degree of warping of the spring provided on the key increases, so that the amount of reaction force applied to the finger increases progressively. Such has been the difference noted of the key operations between the piano and the conventional electronic musical instrument. Thus, the latter instrument has the disadvantages that it lacks the touch-response function exerted by the piano keyboard which faithfully transmits the sentiment of the player to the keys, and accordingly the instrument is difficult to play.
Now, consideration is made of the depressing operation of a key 1 which is equipped with a compression coil spring 2 as shown in FIG. 1. The key 1 normally is held in a substantially horizontal position by the compression coil spring 2 as indicated by a vector P.sub.0. The balancing in the moments when the key 1 is depressed by the application of a force F.sub.1 onto the forward end portion of the key 1 will become as shown by the formula: EQU F.sub.1 L=P.sub.0 l
wherein: L represents the distance from the pivot fulcrum 0 of the key 1 up to the position at which the force F.sub.1 is applied; and l represents the arm of moment exerted by the spring 2.
Hence, EQU F.sub.1 =l/L.P.sub.0 ( 1).
And, the force F.sub.2 when the key 1 is depressed fully to the bottom as indicated by the chain line is: EQU F.sub.2 =l'/L.multidot.P.sub.1 ( 2).
If l.apprxeq.l', the spring pressure will become P.sub.1 &gt;P.sub.0, so that the forces will be: F.sub.2 &gt;F.sub.1. Thus, one can understand the fact that the sence of key touch increases as the key is depressed progressively to a lower position.
Accordingly, in order to provide a light touch of key operation, and to bring the key operation touch closer to the key operation touch of a piano, there is the necessity for satisfying either one of the following three conditions which are derived from the above-mentioned formulas (1) and (2):
(i) in case l=l', there must be P.sub.1 &lt;P.sub.0 ; PA1 (ii) in case P.sub.0 =P.sub.1, there must be l'&lt;l; and PA1 (iii) in case both P.sub.0 and l vary, there must be the relation l'P.sub.1 &lt;lP.sub.0.
However, as stated above, in the prior art, either a compression spring, a tension spring or a U-shape spring has been used. Therefore, the key operation has been performed by making use of compression or pulling of the spring as the case may be. Such mode of key operation has a great difficulty in satisfying the condition (i) or (ii) shown above. Hence, there naturally arises the need to design the keyboard apparatus so as to satisfy the condition (iii).